A number of surgical techniques exist for posterior cervical arthrodesis. Onlay bone grafting and posterior wiring techniques (with or without bone blocks) are currently the most important surgical techniques in this area. These techniques have been supplemented recently by transfacet screw fixation and interlaminar clamp arthrodesis. The interlaminar clamp technique for posterior arthrodesis may prove to be superior to wiring techniques and simpler to perform than screw fixation methods, but the interlaminar clamp technique requires some improvement.
Interlaminar clamp fixation of the cervical spine has been in clinical use for approximately the past decade. Use of interlaminar clamp fixation has proven effective in achieving a satisfactory rate of posterior cervical fusion. There is, however, an incidence on non-union and loosening of the clamp fixation device.
The prior art interlaminar clamp is called a Halifax clamp, and is basically a variation of the common C clamp. FIGS. 19A and 19B show two views of a prior art Halifax clamp. The clamp has two opposing parts, each approximately in the shape of a "C", made out of bent pieces of flat metal bars. Additional representations of these opposing parts are provided in FIGS. 1, 2, 12G and 12H. The upper C-shaped part 1 and the lower C-shaped part 2 are fastened together at one end by a screw 3, which screw 3 is screwed to tighten the clamp. The current design of these prior art clamps is somewhat restricted in that there is a limited variety of clamp sizes and shapes available, which causes incidents of inaccurate fit of the clamps to the laminae. This poor fit problem may result in residual rotatory motion at the operated cervical segment, causing loosening of the clamp and possible disengagement of the clamp from the laminae.
The object of the present invention is to provide a set of new improved interlaminar cervical clamps that provide superior fit and hence do not loosen, and to provide a method to manufacture such clamps. Furthermore, it is an object of this invention to provide a general method of manufacturing better fitting surgical implants of all types.